The present invention relates to a drive arrangement for an aircraft with a propeller, especially with a thrust propeller arranged in the rear fuselage of an aircraft frame which is connected with a drive unit.
In an aircraft with a propeller (DE-PS No. 730 493), a central shaft for the drive is arranged between the propeller and an engine transmission-unit supported on the aircraft frame. The central shaft is rigidly supported in the rear fuselage of the aircraft frame whereby a further rigid fuselage bearing support is provided approximately centrally of the shaft. Such a bearing support is disadvantageous by reason of the rigid connection with the aircraft frame insofar as no body-insulating effect with respect to the aircraft frame can be achieved. Furthermore, with such an arrangement cardan or universal joints are required for the shaft between the propeller and the transmission whose fatigue vibrational loads as a result of relative movements of the engine to the propeller bearing support must be reduced by an interconnected costly slide element.
The present invention is therefore concerned with the task to provide a drive arrangement, essentially consisting of an engine-transmission-unit, of a propeller, and of a shaft, by means of which an arrangement and bearing support of the overall aggregate is realizable which has a favorable vibration behavior. Furthermore, the entire unit is to be installable into the aircraft frame in a simple manner with avoidance of costly adjusting operations.
The underlying problems are solved according to the present invention in that the drive unit is connected with a longitudinally installed tubular support member supportingly accommodating a central shaft and in that the tubular support member as well as the drive unit are supported on the side of the aircraft frame by way of at least three elastic bearing supports whereby the one bearing support is provided at the aircraft rear end of the tubular support member and the two other bearing supports are provided within the area of the drive unit.
The principal advantages achieved with the present invention reside in that a drive aggregate-unit closed in itself and essentially consisting of an engine, a transmission, a thrust propeller and a tubular support member with an inwardly disposed central shaft can be installed in a simple manner into the aircraft frame. The bearing support of this entire aggregate takes place within the area of the rear fuselage part by way of a single elastic bearing support and within the area of the engine-transmission unit by way of two further elastic bearing supports. The bearing supports are preferably located within low-vibration areas of the overall aggregate. These bearing supports are elastically constructed in the vertical and transverse direction for purposes of body-sound insulation and are preferably arranged in a horizontal plane extending through the center of gravity. Furthermore, the bearing supports are supported near the propeller axis in order that the bending stresses of the tubular support member can be kept small.
The shaft is constructed free of joints and with a relatively long construction of the tubular support member is supported sub-critically. With a relatively short shaft, by contrast, no intermediate bearing support of the central shaft is required so that in that case only end side bearing supports are to be provided.
The use of plastic material and/or a light metal for the tubular support member and for the shaft result in a central tubular aggregate light from a weight point of view, whereby with plastic material, a dimensioning corresponding to the occurring loads is possible within wide limits by selected winding angles of the fibers in the plastic material.
For the purpose of the propeller adjustment, a pressure oil line is extended through the hollow central shaft which is retained with respect to the shaft by way of support bearings that are arranged preferably in the plane of the shaft bearings and adjacent thereto and which support the thin and very long line and prevent critical bending vibrations. Additionally, the support bearings avoid an excessively strong constriction of the central shaft when pressing-on the intermediate bearings.
The tubular support member may also consist according to a further embodiment of the present invention of a funnel-shaped transmission cover which extends up to the thrust propeller and in which the central shaft is supported end-side. This transmission cover may also consist of plastic material.
The support bearings of the tubular support member provided in the fuselage rear part may at the same time form a rear cover for the end-face fuselage opening.
The entire aggregate is adjustable as regards bending and torsional vibrations for achieving a best possible operating quiet in the flight rotational speed range by correspondingly selected mass and strength distribution. This is achieved by a suitable selection of the diameter of the central shaft and of the tubular support member, respectively, of the wall thicknesses, whereby also the torsionally soft shaft plate provided within the area of the transmission between the engine and the propeller contributes thereto.